Sep. 6, 2000 (SACRAMENTO, Calif.) -- A UC Davis and Department of Veterans' Affairs Health System study published in the September issue of the Annals of Neurology may be an important advance in helping doctors correctly identify the cause of memory problems in elderly patients. The researchers report that the impact of minor strokes deep in the brain can be distinguished from the damage caused by Alzheimer's disease.
"We found that the brain systems that failed in stroke patients with memory loss were different from those that fail and cause the memory loss of Alzheimer's disease," said Bruce R. Reed, associate director of the UC Davis Alzheimer's Disease Center and lead author of the paper.
If they are alert to what the memory loss of stroke looks like, said Reed, physicians may be able to treat the root cause -- high blood pressure or diabetes -- and thereby prevent strokes.
Diagnosing Alzheimer's disease is difficult enough on its own: it is not obvious where ordinary forgetfulness leaves off and the early stages of Alzheimer's begin. Complicating the diagnosis is evidence accumulated over the past several years, indicating that small strokes deep in the brain may make the memory loss of Alzheimer's worse. These strokes become more common with age, and their role in causing memory problems -- either alone or in conjunction with Alzheimer's -- has been controversial because they often do not occur in "memory" areas of the brain.
Reed and his colleagues studied 15 patients who had suffered small strokes deep in the brain and 15 patients with the diagnosis of mild Alzheimer's disease and compared these patients with similarly aged control subjects. The subjects took memory tests designed to distinguish between different components of memory, including attention to the task and the ability to retrieve memories after longer or shorter test intervals.
The stroke patients were more likely to have problems related to the inability to pay close attention to the task or to remember things after a very short time. Alzheimer's patients, on the other hand, were more likely to have difficulty with retrieving memories after longer intervals.
The researchers also scanned the subjects' brains with positron emission tomography (PET) while the tests were in progress. The scans of stroke patients showed reduced levels of activity in the frontal cortex, a brain area known to be essential for attention. By contrast, the Alzheimer's patients had reduced levels of activity in brain areas (such as the temporal lobe and hippocampus) known to be involved in the coding and storage of memories.
"This shows that it's not simply that stroke pushes people with a little Alzheimer's disease over some sort of threshold for memory loss," said Reed. "The memory loss of deep stroke is more closely related to failures of attention and this makes sense considering the brain circuits that are usually affected by deep strokes. This mechanism had been suspected before, but our data show this very clearly for the first time."
The results point out the importance of being alert for mild memory loss in elderly patients, Reed said. "These problems may not reflect Alzheimer's disease and so it's all the more important to look for and to treat any risk factors for cerebrovascular disease."
This research was supported in part by grants from the National Institute on Aging, the California Department of Health Services Alzheimer's Disease program and the Northern California Veteran Affairs System of Clinics.
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